People have a strong tendency to focus their attention on the center portion of the screen (display screen) of a display device that is displaying a video signal (or image signal). This has led to methods for maintaining the brightness of the center portion of the display screen of the display device while lowering the brightness of the relatively unnoticed surrounding display screen, so as to maintain the sense of brightness of the display screen while concomitantly cutting down on the power that is used by the display device.
These methods achieve a reduction in power consumption by correcting the input video signal so that the luminance drops from about the center of the display screen toward its periphery. Patent Citation 1 is a representative example of such a method.
Patent Citations 2 and 3 are examples of methods for dynamically controlling the extent of luminance drop according to the input video signal, so as to yield further reductions in power consumption.
The technology disclosed in Patent Citation 4 is an example of a technology that, while not intended to reduce power consumption, involves performing appropriate correction of input video (images) according to the state of the input video (images). The technology that is disclosed in Patent Citation 4 is for performing correction based on the content (state) of the input video signal by detecting areas that include images of people's faces from the image data that are formed by the input video (image) signal, and then changing the correction information (correction strength, etc.) based on the result of that detection.
The technology of Patent Citation 4 is primarily intended for the processing of still images, but it can also be adopted for moving images as well. However, adopting the technology of Patent Citation 4 for moving images raises new issues. That is to say, adopting the technology of Patent Citation 4 for moving images usually leads to detection that is incomplete and by and large results in a detection rate that is less than 100%. Adopting the technology of Patent Citation 4 for moving images therefore creates a situation in which there are frames in which an object that is to be detected can actually be detected and those in which it cannot be detected. This leads to variability in the correction outcome when correction is performed according to these detection results. Ultimately, moving images that are processed using the technology of Patent Citation 4 are unstable and may flicker, for example.
In response to this problem, Patent Citation 5, for example, discloses a device that inhibits the sense of instability in a moving image by calculating the current correction information (the correction information that is applied to the current frame) using the correction information from past frames as well. In other words, the technology that is disclosed in Patent Citation 5 inhibits variation in the correction between frames by not only calculating correction information from the information that is based on the detection result but also performing processing so as to minimize change from the correction information from prior frames.